A landed aircraft is in most cases guided firstly into the runway region, in which its parking position is situated, by a vehicle driving in front of it. Painted onto the runway region are so-called center-lines which the aircraft must follow. The center-lines terminate in straight stand-center lines which lead to the parking location.
In appropriately equipped airports, the aircraft dock in the parking position with at least one of their exits at e.g. a gangway bridge. Since such gangway bridges are only movable to a limited extent, it is necessary that the parking position, which is differently determined for each type of aircraft, is adopted exactly. For this purpose, the pilot must stop the aircraft, which is guided on the stand line, at a defined point.
The problem associated with this is that the pilot is located at least 4-6 m above the earth, at least with current aircraft types, and has no direct view downwards.
A range of current accessory equipment (e.g. Moiree indicators) exists which makes it possible for the pilot to guide his aircraft on the stand line without direct visual contact.
The situation is different in connection with systems which are able to give the pilot information relating to the remaining taxiing distance to the parking position. No optimal device has been known up to now in this connection.
It is known e.g. to install induction loops in the ground of the runway which, e.g. as soon as the front wheel of the aircraft rolls over them, produce a signal which can be converted into a corresponding indication of distance. It is disadvantageous that the induction loops can easily suffer damage as a consequence of the large loading by the aircraft which taxi over them or caused by storms, e.g. by lightning strikes, and must be frequently replaced and furthermore also do not function precisely.
A system is also known from WO 90/13104 in which an aircraft approaching its parking position is surveyed by means of radar. This generally occurs with a radar beam based on microwaves which is directed towards the nose of the aircraft. The pilot can find out his actual position or the distance remaining to the parking position by means of an indicator board. It is disadvantageous that the radar beam must be guided to follow the aircraft as it approaches which requires either an optical or some other form of control.